We propose to characterize further the biologic and antigenic, and structural properties of various EBV strains. We will evaluate the tumorigenicity of different strains. We will compare strains with primarily transforming properties with strains which are principally superinfecting. We will attempt to develop quantitative neutralization tests as a basis for antigenic comparisons. In collaboration with experts we will study the structure of EBV DNA and the relatedness of EBV DNA's of diverse origin. We propose a series of experiments to analyze the early events in EBV-induced human lymphocyte transformation. We will make measurements of the proportion of cells which are infected, stimulated to make DNA and transformed following exposure to EBV and to determine whether subpopulations of leukocytes differ in their response to EBV.